(1) Field of the Invention
The invention relates to detergents and rinse agents for machine dishwashing. More particularly, the present invention relates to detergents and rinse agents for machine dishwashing and to supply forms which combine detergent and rinse agent containing certain polymers in a single product. These detergents/rinse agents are generically referred to hereinafter as “detergents for machine dishwashing” or “dishwasher detergents.”
Today, machine-washed tableware has to meet stricter requirements than hand-washed tableware. Thus, even tableware completely free from food residues is regarded as unsatisfactory when, after dishwashing, it still has whitish stains which are attributable to water hardness or other mineral salts and which come from water droplets that have remained on the tableware through lack of wetting agent and dried.
Accordingly, to obtain bright, spotless tableware, rinse agents are now successfully used. The addition of rinse agent at the end of the wash program ensures that the water drains completely from the tableware so that the various surfaces are bright and free from residues at the end of the dishwashing program.
The cleaning of tableware in domestic dishwashing machines normally comprises a pre-rinse cycle, a main wash cycle and a final rinse cycle which are interrupted by intermediate rinse cycles. With most machines, the pre-rinse cycle can be selected for heavily soiled tableware, but is only selected by the consumer in exceptional cases so that, in most machines, a main wash cycle, an intermediate rinse cycle with clean water and a final rinse cycle are carried out. The temperature of the main wash cycle varies between 40 and 65° C., according to the type of machine and the program selected. In the final rinse cycle, rinse aids which normally contain nonionic surfactants as their main constituent are added from a dosing tank. These rinse aids are liquids and are widely described in the prior art. Their principal function is to prevent lime stains and bloom on the cleaned tableware. Besides water and low-foaming nonionic surfactants, many rinse aids often contain hydrotropes, pH regulators, such as citric acid, or bloom-inhibiting polymers.
(2) Description of Related Art, Including Information Disclosed Under 37 C.F.R. §§ 1.97 and 1.98
EP-B1 0 197 434 (Henkel) describes liquid rinse agents which contain mixed ethers as nonionic surfactants. A wide variety of materials (glass, metal, silver, plastic, china) is cleaned in dishwashers. These various materials have to be thoroughly wetted in the final rinse cycle. Rinse agent formulations containing only mixed ethers as their surfactant component satisfy these requirements inadequately, if at all, so that the clear rinse effect or drying effect is unsatisfactory, particularly on plastic surfaces.
The storage tank in the dishwashing machine has to be filled with rinse agent at regular intervals, one filling being enough for 10 to 50 rinse cycles according to the type of machine. If the consumer forgets to fill the tank, glasses in particular are spoiled by lime stains and bloom. Accordingly, some proposals have been put forward in the prior art with a view to integrating a rinse agent in dishwasher detergents. These proposed solutions are confined to tablets.
Thus, European patent application EP-A-0 851 024 (Unilever) describes two-layer detergent tablets of which the first layer contains peroxy bleaching agent, builder and enzyme while the second layer contains an acidifying agent, a continuous medium with a melting point of 55 to 70° C. and bloom inhibitors. The high-melting continuous medium is said to release the acid(s) and bloom inhibitor(s) with delay and to develop a clear rinse effect. Powder-form dishwasher detergents or surfactant-containing rinse agent systems are not mentioned in this document.